1. FIELD OF THE INVENTION
This invention relates to a process for preparing gypsum wallboard or plasterboard and to an apparatus for use in the process.
2. DESCRIPTION OF THE PRIOR ART
Although gypsum wallboards and plasterboards possess excellent characteristics in such properties as fireproofness, heat insulation, and dimensional stability, it is desired also to obtain further improvements in the bending strength, impact strength and water-permeability thereof. Heretofore, it has been difficult to obtain gypsum board products possessing high levels of all these desired properties.
For improving the properties of gypsum board, such as the bending strength and impact strength, it has been proposed to blend a fibrous material such as paper pulp, asbestos,, rock wool, glass fibre or synthetic resin fiber into the starting calcined gypsum material.
However, the addition of large amounts of such fibrous materials into the starting calcined gypsum lowers the mechanical strength of the board product, because a large amount of water must also simultaneously be incorporated into the starting mixture. If the amount of water incorporated is reduced in such a case, the ease of workability of the process is reduced and homogeneous distribution of the plaster and the fiber in the mixture is inhibited, whereby the fiber is non-uniformly dispersed in the resulting board product.
As the result of these disadvantages, the properties of the board product are not appreciably improved by these techniques.